Elucidating the roles of the Fe-Nx active sites and pore characteristics on Fe-Pani-biomass-derived RGO as oxygen reduction catalysts in PEMFCs

Pyrolysed Fe-N-C catalysts are foreseen to be promising noble-free cathode catalysts for proton exchange membrane fuel cells. Nevertheless, efforts are required to overcome active site degradation, which is influenced by the meso/macroporous composition of the catalyst and support. Reduced graphene oxide from Sengon wood is seen as a potential support for Fe-polyaniline (Pani) catalysts due to its hierarchical porous structure that depends on N/C ratio. This work reveals that the Fe-N4 moiety serves as the active site, which is confirmed by XPS and first-principles calculations. Fe-Pani-RGO 2:0.2, with the highest content of Fe-N4 and specific surface area, results in the highest ORR activity with Eonset =0.84 V, E1/2 = 0.79 V, and JD = 5.5 mA/cm2. Although micropores are important for hosting the active sites that contribute to high ORR activity, in regard to single-cell performance, the role of meso‑/macropores is crucial for achieving higher overall performance.